Most of the concern about mercury focuses on lakes and other aquatic ecosystems, such as rivers, streams, wetlands and oceans. The levels of mercury found in terrestrial environments are usually not high enough to threaten the health of wildlife and humans. But some aquatic environments favour the transformation of mercury into its more poisonous form — methylmercury — and it is the bioac- cumulation of methylmercury in fish and marine mammals that presents a potential problem when they are consumed by humans. In addition to human health effects, many predatory species of fish and wildlife, which rely on fish for food, are at risk of mercury.
